EP0532995A2 - Process for preparing polysaccharide carbonates - Google Patents

Abstract

The present invention relates to a process for the preparation of carbonic esters of polysaccharides which is characterised in that polysaccharides are reacted with carbonic esters.

Description

The present invention relates to a process for the preparation of carbonic acid esters of polysaccharides, which is characterized in that polysaccharides are reacted with carbonic acid esters.

Carbonic acid esters of polysaccharides are interesting materials with a number of possible uses, e.g. as depots for bioactive compounds (see Makromol. Chem. 186, 17-29 (1985), for fixing enzymes for carrying out enzymatic reactions in a heterogeneous phase (see ICS Perkin I 1974, 757 -762, or Biochemistry Internat. 4 ( 1982 629-635, or US Pat. No. 3,810,821), also as starting products for coating raw materials, thickeners for aqueous solutions and suspensions, for example in the construction industry or for adhesive raw materials ( see U.S. Patent 3,284,442 and U.S. Patent 4,097,667).

For these reasons, there has been no shortage of efforts to make these substances accessible in various ways.

All of the processes known to date introduce the carbonate residue via particularly reactive carbonic acid derivatives, usually chlorocarbonic acid esters. This also appears to make sense, since the known low reactivity of polysaccharides - evident from the normally long reaction times - is to be compensated for by the use of reactive reagents (cf. US Pat. No. 3,284,442, 3,810,821, 4,097,667 and Carbohydrate Research 17 (1971 ), the literature already cited above). These reactions are often carried out in the presence of hydroxyl compounds, such as water or alcohols, or in the presence of expensive solvents. A large part of the chlorocarbonic acid esters are consumed in side reactions with water or alcohol. The expensive solvents are difficult to recover from the complicated reaction mixtures. The hydrogen chloride liberated in the reaction must be bound by bases and the commonly used organic nitrogen base must be released from its salts and reused. These processes are therefore very time-consuming. In addition, only a low degree of substitution (DS) is achieved, which is often not sufficient for the applications mentioned.

An exception to this is DE-OS 3 836 600, according to which very high DS can be obtained. But here, too, you have to use chlorocarbonic acid esters.

According to the currently known prior art, no simple and efficient process for the preparation of carbonic acid esters of the polysaccharides is available can be carried out with a very high reagent yield and without waste products and leads to high degrees of substitution.

It has now been found that carbonic acid esters of polysaccharides can be obtained in a simple and elegant manner by transesterifying them with carbonic acid esters.

worin R¹ und R² gleich oder verschieden sind und C₁-C₁₂-Alkyl, vorzugsweise C₁-C₈, besonders bevorzugt C₁-C₄-Alkyl, Allyl- und Methallyl, Benzyl, Phenyl, Kresyl oder R¹ und R² zusammen mit der Carbonatgruppe einen Ring mit insgesamt 5 bis 12 Ringgliedern darstellen, wobei darin R¹ und R² sind:

-(CH₂)_n-

mit n = 2 - 10, bevorzugt 2 - 6, besonders bevorzugt 2 und 3

mit R³ = CH₃, C₂H₅, Phenyl, CH₂-Cl, vorzugsweise CH₃

mit R⁴ und R⁵ gleich oder verschieden

-CH₂-O-CH₂-CH = CH₂
vorzugsweise CH₃,CH₂OH,CH₂O-CH₂CH = CH₂ besonders bevorzugt CH₃

-(CH₂-CH₂-O)_n-CH₂-CH₂-

mit n = 1 - 3, bevorzugt 1 - 2

bei Temperaturen zwischen 40 - 160°C, gegebenenfalls in Gegenwart von Katalysatoren umestert.The invention therefore relates to a process for the preparation of carbonates of the polysaccharides, which is characterized in that polysaccharides with carbonic acid esters of the general formula I

wherein R¹ and R² are the same or different and C₁-C₁₂ alkyl, preferably C₁-C₈, particularly preferably C₁-C₄ alkyl, allyl and methallyl, benzyl, phenyl, cresyl or R¹ and R² together with the carbonate group a ring with a total 5 to 12 ring members, wherein R¹ and R² are:

- (CH₂) _n -

with n = 2-10, preferably 2-6, particularly preferably 2 and 3

with R³ = CH₃, C₂H₅, phenyl, CH₂-Cl, preferably CH₃

with R⁴ and R⁵ the same or different

-CH₂-O-CH₂-CH = CH₂
preferably CH₃, CH₂OH, CH₂O-CH₂CH = CH₂, particularly preferably CH₃

- (CH₂-CH₂-O) _n -CH₂-CH₂-

with n = 1-3, preferably 1-2

at temperatures between 40 - 160 ° C, optionally transesterified in the presence of catalysts.

This is surprising because after the known long reaction times with the highly reactive chlorocarbonic acid esters it was to be expected that the substantially less reactive carbonic acid esters would at most lead to significant sales in technically completely unacceptable times.

In contrast, high degrees of transesterification are obtained in relatively short reaction times. The method according to the invention offers particular advantages in that it is completely free of waste products. During the transesterification with the polysaccharides, the carbonic acid esters of the formula I only provide the hydroxyl compounds on which the esters are based, which can be separated off by distillation and used again in the process for the preparation of the carbonic acid esters of the formula I.

According to US Pat. No. 3,810,821, reactions of polysaccharides with chloroclenic acid esters, in addition to the open carbonates, are also often cyclic to a large extent even predominantly educated. This is disadvantageous in that two OH groups are bound in each case by the formation of cycles and the substitution sites on the polysaccharide are thus reduced. In a subsequent reaction of such a cyclic polysaccharide carbonate with amino groups, for example an enzyme to be bound, a cyclic carbonate is always cleaved with the regression of an OH group and formation of only one urethane group, so theoretically only 50% of a cyclic carbonate can be removed an open carbonate group, however, up to 100% urethane are formed. The substitution options for open carbonates are therefore much cheaper.

The carbonates obtainable by the process according to the invention contain practically no cyclic carbonates and are therefore substituted more uniformly than the previously available and more advantageously used for further reactions.

Starting materials:

Suitable starting materials for the preparation of the polysaccharide carbonates according to the invention are, for example, polyglucosans, such as cellulose; the various derivatives of cellulose, such as methyl cellulose; or mixed cellulose ethers such as methyl-hydroxyethyl cellulose, carboxymethyl cellulose and their various salts with sodium, potassium, calcium or ammonium, especially quaternary ammonium ions; Cellulose sulfate with various counterions such as sodium, potassium, calcium, ammonium and quaternary ammonium groups; Starch, dextrins, glycogen; Polyfructosans such as inulin and graminin; Polymannosans, Polygalactosans; also mixed polysaccharides, such as hemicelluloses, also polyxylosans and polyarabinosans, and also heteropolysaccharides, such as gellan, xanthan and pullulan.

Preferred starting products are cellulose and its derivatives, starch and dextrins; cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose and their salts and starch are particularly preferred.

-(CH₂)_n-

mit n = 2 - 10, bevorzugt 2 - 6, besonders bevorzugt 2 und 3

mit R = CH₃, C₂H₅, Phenyl, CH₂-Cl, vorzugsweise CH₃

mit R⁴ und R⁵ gleich oder verschieden

-CH₂-O-CH₂-CH = CH₂
vorzugsweise CH₃,CH₂OH,CH₂O-CH₂CH = CH₂ besonders bevorzugt CH₃

-(CH₂-CH₂-O)_n-CH₂-CH₂-

mit n = 1 - 3, bevorzugt 1 - 2

Genannt seien z.B. Dialkylcarbonate, wie Dimethyl-, Diethyl-, Dipropyl-, Diisopropyl-, Dibutyl-, Diisobutyl-, Dicyclohexyl-, Dioctyl-, Didodecyl-, Diisooctyl- und Diisononylcarbonat, unsymmetrische Vertreter, wie Methylethyl-, Methylisopropyl-, Methylcyclohexyl- oder Ethylbutylcarbonat, bevorzugt sind jedoch symmetrische Carbonate. Von diesen wiederum sind besonders bevorzugt Dimethyl-, Diethyl-, Dipropyl- und Dibutylcarbonat; ganz besonders bevorzugt sind Dimethyl- und Diethylcarbonat. Genannt sind weiterhin Benzylcarbonate, wie Methylbenzylcarbonat, Ethylbenzylcarbonat und Dibenzylcarbonat, Diallyl- und dimethylallylcarbonat, Diphenylcarbonat, Di-p-kresylcarbonat, Di-o-kresylcarbonat, ferner Ethylen- und Propylencarbonat, Trimethylencarbonat, 4-Phenyldioxolanon, 4-Ethyldioxolanon,

5,5-Dimethyl-1,3-dioxanon-2, 5-Ethyl-5-hydroxymethyl-1,3-dioxanon-2, 5-Ethyl-5-allyloxy-1,3-dioxanon-2

5-Ethyl-5-benzyloxy-1,3-dioxanon-2, schließlich cyclische Carbonate aus Polyglykolen, wie Diglykol, Triglykol und Tetraglykol.Suitable carbonic acid esters are those of the formula I in which R¹ and R² are identical or different and are C₁-C₁₂-alkyl, preferably C₁-C₈, particularly preferably C₁-C₄-alkyl, allyl and methallyl, benzyl, phenyl, cresyl or R¹ and R² together represent a ring with the carbonate group with a total of 5 - 12 ring members, in which R¹ and R² are:

- (CH₂) _n -

with n = 2-10, preferably 2-6, particularly preferably 2 and 3

with R = CH₃, C₂H₅, phenyl, CH₂-Cl, preferably CH₃

with R⁴ and R⁵ the same or different

-CH₂-O-CH₂-CH = CH₂
preferably CH₃, CH₂OH, CH₂O-CH₂CH = CH₂, particularly preferably CH₃

- (CH₂-CH₂-O) _n -CH₂-CH₂-

with n = 1-3, preferably 1-2

Examples include dialkyl carbonates such as dimethyl, diethyl, dipropyl, diisopropyl, dibutyl, diisobutyl, dicyclohexyl, dioctyl, didodecyl, diisooctyl and diisononyl carbonate, unsymmetrical representatives such as methylethyl, methylisopropyl, methylcyclohex or ethyl butyl carbonate, but preferred are symmetrical carbonates. Of these, in turn, dimethyl, diethyl, dipropyl and dibutyl carbonate are particularly preferred; dimethyl and diethyl carbonate are very particularly preferred. Also mentioned are benzyl carbonates, such as methylbenzyl carbonate, ethylbenzyl carbonate and dibenzyl carbonate, diallyl and dimethylallyl carbonate, diphenyl carbonate, di-p-cresyl carbonate, di-o-cresyl carbonate, furthermore ethylene and propylene carbonate, trimethylene carbonate, 4-phenyldioxolanone, 4-ethyldioxolanone,

5,5-dimethyl-1,3-dioxanone-2, 5-ethyl-5-hydroxymethyl-1,3-dioxanone-2, 5-ethyl-5-allyloxy-1,3-dioxanone-2

5-ethyl-5-benzyloxy-1,3-dioxanon-2, finally cyclic carbonates from polyglycols, such as diglycol, triglycol and tetraglycol.

The simple dialkyl carbonates, diphenyl carbonate, ethylene carbonate, 1,2-propylene carbonate, 1,3-propylene carbonate, 2,2-dimethyl-1,3-propylene carbonate, 2-ethyl-2-hydroxymethyl-1,3-propylene carbonate are preferred , 2-ethyl-2-allyloxy-1,3-propylene carbonate.

In principle, the reaction can be carried out without a catalyst. As a rule, however, it is advantageous and shortens the duration of the transesterification if a catalyst is used. Suitable catalysts are compounds of alkali and alkaline earth metals, zinc, cobalt, titanium, zirconium, thallium, lead and tin as well as organic bases such as nitrogen bases and their quaternization products.

The compounds of these metals which may be mentioned are the hydrides, the hydroxides, oxides, carbonates, alcoholates, such as methylates, ethylates, isopropylates, butylates, dodecylates, sulfates, nitrates; Carboxylates, such as acetates, propionates, benzoates or stearates, the halides, rhodanides, cyanides and, in the case of tin, also alkyl, dialkyl and trialkyl or phenyltin chlorides, carboxylates, alcoholates, oxides or hydroxides; Compounds of alkali metals, zinc, tin and titanium are preferred as hydroxides, oxides, carbonates, alcoholates, carboxylates and in the case of tin as mono-, di- and trialkyltin oxides, hydroxides, carboxylates and alcoholates.

Suitable bases for the preparation of the polysaccharide carbonates according to the invention are tertiary nitrogen bases from the aliphatic, aromatic and heterocyclic series, such as trimethylamine, triethylamine, tributylamine, dimethylcyclohexylamine, diisopropylethylamine, dicyclohexylmethylamine, dimethyl-β-methoxyethylamine, N, N, N ', N'-tetramethylethylenediamine, N, N, N', N'-tetramethyl-β, β'-diamino-diethyl ether, N; N'-dimethylpiperazine, N-methylmorpholine and diazabicylooctane, N, N'-dimethylaniline, N, N-diethylaniline, N, N, N ', N'-tetramethyldiaminobenzene, N, N-dimethyltoluidine, N, N-diethylxylidine, N, N-dimethylanisidine and N-phenylmopholine, pyrazole, N-alkylpyrazole, imidazole, N- Methylimidazole, triazole, N-ethyltriazole, N, N-dimethylamino-imidazole, N, N-diethylamino-triazole, pyridine, α, β-, -picolin, the lutidines, collidine, ethylmethylpyridines, N, N-dialkylaminopyridines, such as N, N-dimethyl-4-aminopyidine, quinoline, methylquinoline and isoquinoline.

Preferred are diazabicyclundecen, diazabicyclonones, triethylamine, dimethylcyclohexylamine, methylmorpholine, dimethylpiperazine and diazabicyclooctane, tetramethylethylenediamine, triazole, aminotriazole, diethylaminotriazole, imidazole, N-methylimidazole, N, N-dimolinolidino, methyl, imidazolino and methyl, N, N-dimolinamidino, methyl, imidazolino and N, N-dimethylamido, the methyl, N, N-dimethylamido.

The process is advantageously carried out at elevated temperature. It is 40 to 160 ° C, preferably 60 to 150 ° C, particularly preferably 70 to 140 ° C.

You can work under different pressures, in the range from 0.1 mbar to 10 bar, preferably from 1 mbar to 5 bar, particularly preferably from 2 mbar to 3 bar. As a rule, it can be transesterified at atmospheric pressure. If the hydroxy compounds formed are to be removed during the transesterification, a reduced pressure may be indicated, and if the transesterification is carried out with low-boiling dialkyl carbonates, a higher pressure is indicated.

In many cases, the reaction can be carried out in the carbonic acid esters used as the reaction medium. However, if only a small amount of carbonic acid ester is to be used or if the carbonic acid ester has a relatively high melting point, then the use of a solvent as a thinner and suspending agent or solvent for the polysaccharide is recommended.

Suitable solvents or suspending agents are, for example, cyclohexane, pentane, heptane, isooctane, benzene, toluene, methylene chloride, chloroform, dichloroethane, trichlorethylene, chlorobenzene, dichlorobenzene, bromobenzene, diethyl ether, diisopropyl ether, dibutyl ether, dioxane, benzodioxkane, anisole ethylglycol, ethylene glycol, ethylene glycol, dimethylene glycol, ethylene glycol, ethylene glycol, dimethylene glycol, ethylene glycol, ethylene glycol, dimethylene glycol, ethylene glycol, dimethylene glycol, ethylene glycol, ethylene glycol, dimethylene glycol, ethylene glycol, dimethylene glycol, ethylene glycol, ethylene glycol, dimethylene glycol, ethylene glycol, ethylene glycol, ethylene glycol, dimethylene glycol, ethylene glycol, ethylene glycol, dimethylene glycol, ethylene glycol, ethylene glycol, ethylene glycol, ethylene glycol, ethylene glycol, ethylene glycol, ethylene glycol, ethylene glycol -di-methyl ether, ethyl acetate, butyl acetate, ethyl propionate, ethyl butyrate, ethyl benzoate, diethyl malonate, diethyl succinate, acetone, methyl ethyl ketone, diethyl ketone, methyl isopropyl ketone, acetophenone, cyclohexanone, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl methyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl formamide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl amide, dimethyl formamide , N-dimethyl-2,6-diaza-4-oxa-cyclohexanone, N-methylpyrrolidone, N-methylcaprolactam, acetonitrile, β-methoxy-propionitrile and β-cyano-β'-methoxy-diethyl ether.

In principle, the polysaccharide can be implemented in dissolved form. This is usually associated with large reaction volumes. It is therefore preferred to work in suspension or dispersion. As described above, the carbonic acid esters to be used or the solvents specified above are used as dispersants.

The molar ratio of carbonic acid ester to polysaccharide is not critical and can vary between 100: 1 to 1:20, preferably 80: 1 to 1:15, particularly preferably 60: 1 to 1:10.

The degree of substitution of the polysaccharide can be influenced under otherwise identical conditions by the amount of carbonic acid ester offered or its dilution by solvent or dispersing agent, by the reaction time and type and amount of catalyst used, the degree of substitution becoming higher the more carbonic acid ester or The more active the catalyst and the longer the reaction time, which is between 0.5 to 40 h, preferably 1 to 30 h, particularly preferably 1 to 25 h, is used.

To carry out the transesterification, the polysaccharide, the carbonic acid ester (and optionally a dispersing agent) are added in such an amount that a readily stirrable dispersion is formed, together with the optionally provided catalyst heated to the reaction temperature with stirring. Depending on its boiling point and the conditions set, the hydroxy compound formed can be removed from the reaction mixture by distillation or else remain in the reaction mixture. The progress of the reaction can be determined by IR spectroscopic analysis of polysaccharide samples, by determining their CO₂ content, by saponification or by gas chromatographic determination of the hydroxy compounds formed.

After the transesterification has ended, the polysaccharide carbonate is filtered off with suction, optionally washed and dried.

The filtrate can be worked up by distillation, excess carbonic acid ester in the transesterification and the hydroxy compound in the carbonic acid ester synthesis can be returned.

In some cases, for example in the case of celluloses of different origins, the polysaccharide should be pretreated in order to open it up for the transesterification. Such digestion can be carried out by the usual methods by the action of sodium hydroxide solutions, ammonia, amines and quaternary ammonium compounds (see Ullmanns Encyclopedia 4th Edition Vo. 5a p. 383 ff). The solubilizers can be displaced by solvents and these by the carbonic acid esters. However, parts of the disintegrants can also remain as catalysts in the polysaccharide. Also by displacing the disintegration agents Inclusion celluloses formed with solvent (see Ullmann's lc) can be used for the transesterification.

The subject matter of the invention will be explained in more detail with the aid of the following examples.

example 1

137 g of a commercially available spruce cellulose were stirred with an aqueous isopropanol solution of about 2 l containing 76 g of NaOH for a few hours at 25 ° C., suction filtered and washed with alkali-free methanol, suction filtered and methanol was displaced with dimethyl carbonate.

100 g of this moist cellulose was refluxed for 3 hours with about 1 liter of dimethyl carbonate and 1 g of potassium hydroxide. After suction, repeated thorough washing with methanol and drying at 50 ° C in a vacuum, 75 g of methyl carbonate cellulose with a CO₂ content of 4.5 wt .-% and a clear CO band in the IR spectrum remained at 1755 cm⁻¹. After briefly boiling out the carbonate cellulose with methanol, there were no changes in the intensity and position of the band.

Example 2

100 g of the moist spruce cellulose pretreated as in Example 1 were kept at 84 ° C. for 6 hours with 1 l of dimethyl carbonate and 5 g of KOH while methanol and dimethyl carbonate were distilled off. After suction and thorough washing with water and then isopropanol and drying at 50 ° C in a vacuum, 73 g of methyl carbonate cellulose with a CO₂ content of 8.2 wt .-% and a considerable CO absorption in the IR spectrum at 1756 cm⁻¹ .

Example 3

Example 2 was repeated, the reaction time being increased to 10 h. A methyl carbonate cellulose was obtained with a CO₂ content of 12.9% by weight.

Example 4

137 g of a commercially available spruce cellulose are activated as in Example 1 with aqueous isopropanolic sodium hydroxide solution, the sodium hydroxide solution is displaced with isopropanol and this is in turn exchanged for cyclohexane.

100 g of this inclusion cellulose containing cyclohexane were transesterified with 800 g dimethyl carbonate and 0.4 g NaOH for 10 h as in Example 2, suction filtered, washed with isopropanol and dried. 49 g of methyl carbonate cellulose were isolated: CO₂ content 15 wt .-% strong CO band in the IR spectrum at 1755 cm⁻¹.

Example 5

100 g of potato starch were stirred with 500 ml of dimethyl carbonate and 0.5 g of KOH at 80 ° C for 6 h. After suction, washing with isopropanol and drying, 90 g of methyl carbonate starch with a pronounced CO absorption in the IR spectrum at 1751 cm -1 was obtained.

Example 6

42 g of a hydroxyethyl cellulose with a DS of about 1.1 was mixed with 400 ml of dimethyl carbonate and 0.4 g of KOH Stirred at 84 ° C for 6 h. After separating off the dimethyl carbonate, washing with isopropanol, water and finally methanol and drying, 41 g of a hydroxyethylmethyl carbonate cellulose with a CO₂ content of 8.0% by weight and a strong CO band in the IR spectrum remain at 1757 cm⁻¹.

Example 7

100 g of a commercially available hydroxyethyl cellulose with a DS of 1.1 was heated with 400 g of diphenyl carbonate and 0.5 g of KOH at 120 ° C. for 1 hour while distilling off phenol at 1.4 mbar. The residue was taken up in isopropanol and washed thoroughly several times with isopropanol. After drying remained 105 g with a CO₂ content of 11 wt .-% and a strong CO band in the IR spectrum at 1762 cm⁻¹.

Example 8

100 g of a commercially available carboxymethyl cellulose Na salt were stirred at 110 to 120 ° C. for 6 hours with 100 g of ethylene carbonate and 2.5 g of imidazole in 500 ml of chlorobenzene. After suction, washing with isopropanol and drying, 106 g of a carboxymethyl cellulose carbonate with a clear CO absorption in the IR spectrum remained next to the carboxylate band.

Example 9

100 g of a spruce cellulose (moist), as activated in Example 1, 200 g of ethylene carbonate and 0.5 g of KOH stirred in about 300 ml of chlorobenzene at 100 to 110 ° C for 4 h. After suction, thorough washing with isopropanol and drying, a carbonate cellulose with a pronounced CO absorption in the IR spectrum at 1746 cm⁻¹ was obtained.

Example 10

100 g of a commercially available hydroxyethyl cellulose were stirred with 1 l of dimethyl carbonate and 5 g of KOH at 80 ° C. for 12 h while distilling off methanol-dimethyl carbonate mixtures. After working up by suction, washing with isopropanol and drying, 132 g remained with a CO₂ content of 21.2% by weight.

Claims (3)

Process for the preparation of polysaccharide carbonates, characterized in that polysaccharides are reacted with carbonic acid esters. Process according to claim 1, characterized in that polysaccharides with carbonic acid esters of the general formula I

wherein R¹ and R² are the same or different and C₁-C₁₂ alkyl, preferably C₁-C₈, particularly preferably C₁-C₄ alkyl, allyl and methallyl, benzyl, phenyl, cresyl or R¹ and R² together with the carbonate group a ring with a total Represent 5 to 12 ring members, transesterified at temperatures between 40-160 ° C, optionally in the presence of catalysts. Process according to one of claims 1 or 2, characterized in that the reaction is carried out in the presence of compounds of alkali metals, alkaline earth metals, zinc, cobalt, titanium, zirconium, thallium, lead, tin and / or in the presence of nitrogen bases or their quaternization products .